Halide-containing polymers such as chlorine-containing polymers (ie such as polyvinyl chloride (PVC)) may be thermally unstable. PVC is one of the most important large-volume thermoplastics available in the market. It is also one of the least thermally stable polymers in commercial use. In PVC processing and the subsequent end uses of PVC, heat stabilisers are needed.
A range of additives can be used to stabilise PVC and such PVC stabilisers can be classified into four categories, namely:                lead stabilisers;        tin stabilisers;        mixed metal stabilisers; and        organic stabilisers.        
Lead stabilisers are stabilisers having lead derivatives as the primary stabilising ingredients, which include inorganic salts such as lead tribasic sulfate, lead dibasic phosphite, etc, and lead soaps, such as, for example, stearates, laurates, etc. Lead stabilisers are currently the market dominant stabilisers for PVC.
Tin stabilisers are stabilisers containing alkyl-tin mercaptides or carboxylates as the primary stabilising ingredients. The tin stabilisers are commonly used in stabilising rigid PVC.
Mixed metal stabilisers are stabilisers containing a combination of metal carboxylates such as barium-zinc or calcium-zinc carboxylates. The mixed metal stabilisers containing calcium-zinc carboxylates are an alternative to lead stabilisers and/or tin compound.
Organic stabilisers are stabilisers containing metal-free organic compounds as the primary stabilising agents. Organic stabilisers are free of lead, cadmium, tin, barium, antimony, zinc and other heavy metals.
Commercially, lead is still today's worldwide dominant PVC stabiliser for due to the properties of lead. Due to environmental regulations prohibiting lead, it is desirable that lead be phased out from application in lead stabilisers. Lead-substitutes, which are environmentally friendly and acceptable, fall under two categories, that is calcium-zinc (Ca/Zn) and heavy-metal-free organic based stabilisers. However, zinc chloride, which is generated in PVC stabilised by a Ca/Zn stabiliser in the PVC processing step, is regarded as a toxic substance.
In view of the above, there is a need to provide a stabiliser for thermally stabilising chlorine-containing polymers.
There is also a need to provide a stabiliser that overcomes or at least ameliorates one or more of the disadvantages described above.
There is a need to provide an organic based stabiliser for chlorine-containing polymers such as PVC, which is free from lead, cadmium, tin, barium, antimony, zinc and any other heavy metals.